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ABSTRACT
CD14 and Toll-like receptor 4/MD2 (TLR4/MD2) mediate the action of LPS on neutrophils. The anti-CD14 antibody and the TLR4/MD2-antagonist, synthetic lipid IVa (LA-14-PP), are known to inhibit the response of neutrophils to LPS. We studied the role of CD14 in LPS-induced priming of neutrophils for enhanced release of the superoxide anion. The anti-CD14 antibody at much higher concentrations than required to saturate CD14 was required to inhibit priming by LPS. The inhibitory effect of the anti-CD14 antibody was overcome by LPS. After washing, anti-CD14-treated neutrophils showed upregulated CD14 upon incubation at 37°C and responded to LPS with a delayed time-course. Thus, CD14-blocked neutrophils gained responsiveness to LPS through newly upregulated CD14. These results suggested that the unbound/free anti-CD14 antibody was essential to inhibit LPS-induced priming by blocking CD14 that were newly expressed during incubation at 37°C. LA-14-PP inhibited the response of neutrophils to LPS in an anti-CD14 antibody sensitive manner. When neutrophils were treated with LA-14-PP followed by treatment with the anti-CD14 antibody, CD14 was upregulated upon warming, but priming was blocked, suggesting that TLR4/MD2 was not newly expressed by warming in association with CD14 molecules. Thus, in addition to blocking CD14, the anti-CD14 antibody was found to induce the expression of new CD14.
Acknowledgments
We thank Floyd C. McIntire for providing E. coli LPS.
Declaration of interest
The authors declare that they have no conflict of interest.
Funding
This work was supported by Grant-in-Aid 26463136 to T.S. from the Ministry of Health of Japan.
